1. Field of the Invention
The present invention relates to an optical disk reproduction apparatus for reproducing an optical disk on which address information is recorded due to a wobble modulation being applied to an information recording track, and an optical disk reproduction method.
2. Description of the Related Art
As well known, in recent years, a technique of recording information at a high density has been developed, and an optical disc having a recording capacity of 4.7 GB (Giga Byte) on one side has been put to practical use.
As such an optical disc, there are DVD-ROMs (Digital Versatile Disk-Read Only Memory) which are a reproduction-only type, DVD-RAMs (Random Access Memory), DVD-RWs (Rewritable), DVD+RWs which are a rewritable type, and DVD-Rs which are a write-once type, or the like.
This type of optical disk carries out recording-reproduction of information by condensing a laser light onto an information recording layer formed on a transparent substrate. In this case, a track formed from a physical concave portion or convex portion is formed on the information recording layer of the optical disk, and the recording-reproducing of information is carried out along this track.
Further, a physical address, which is positional information for specifying a three-dimensional position at which information is recorded and reproduced, is recorded on the track. In a DVD-RAM, recording of a physical address is carried out by forming pre-pits formed from minute concave/convex at each predetermined track length.
In contrast thereto, in a DVD+RW, a physical address is recorded by utilizing so-called wobble modulation in which a track is made to meander (wobble) slightly in the radial direction of the optical disk, and frequency modulation or phase modulation is applied to the wobble.
Such means for recording a physical address due to the wobble modulation can broadly occupy a region on which user information is recorded because the track is not cut off as compared with means for forming pre-pits on the way of the track, and has the advantage that formatting efficiency is high, and the advantage that it is highly compatible with a reproduction-only medium.
In order to reproduce an physical address from the wobble to which phase modulation has been applied, there is a technique in which, after a wobble waveform which has been phase-detected by using a synchronous detecting method, a delay detecting method, or the like is made to pass through an integrator, an LPF (Low Pass Filter), or the like, it is determined a binary code denoting an physical address due to the wobble waveform being compared with a predetermined threshold value.
Further, there is a technique in which a physical address is reproduced by directly integrating a wobble signal by using a clock synchronous with the wobble. For example, in Jpn. Pat. Appln. KOKAI Publication No. 2001-209937, a phase detection signal is integrated for a predetermined interval zone by an integral timing signal, and phase modulation is carried out by comparing the output value with a fixed threshold value.
However, in the art of Jpn. Pat. Appln. KOKAI Publication No. 2001-209937, because the integral value of the phase detection signal is compared with a predetermined fixed threshold value, there is the possibility that an error of determining a code of a physical address arises when a level of the phase detection signal fluctuates, or the like.
In an optical disk such as a DVD-R, in which recording-reproduction is carried out by a CLV (Constant Linear Velocity) system, the phase relationships of the wobbles between adjacent tracks differ in accordance with the radial position.
Therefore, a phase and an amplitude of a wobble signal reproduced from a predetermined track fluctuates in accordance with the crosstalk due to the wobbles of the adjacent tracks. If the phase and the amplitude of the wobble signal fluctuates, because asymmetry arises in the waveform due to the amplitude and the central level of the phase detection signal being fluctuated, there is the possibility that an error of determining a binary code arises in comparison with a fixed threshold value.